1. Field of the Invention
The present invention relate to an oil strainer, for example, provided in an oil circulation system of an automatic transmission and the like of automobiles.
2. Description of the Conventional Art
FIGS. 4 (a)-4(b) show a typical oil strainer of the conventional art which is provided in an oil circulation system of a automatic transmission and the like of automobiles, wherein FIG. 4(a) is a plan view of the oil strainer, and FIG. 4(b) is a sectional view taken along the lines in FIG. 4(a).
The oil strainer shown in FIGS. 4(a)-4(b) is provided with a case 100 comprising a lower case 101 having an inflow opening 101a and an upper case 102 having an outflow opening 102a that opens at a different planar position from the inflow opening 101a, and a pouch-like filter member 103 formed by folding a sheet of the filtering material is disposed in an internal space of the case 100. An opening portion 103a formed at the lower folded section is joined to the inflow opening 101a of the lower case 101 by heat-seal or the like, and a peripheral portion of the upper case 102 and a peripheral portion of the lower case 101 are joined together in the state that the overlapped peripheral portions 103b are sandwiched between and secured by them. A plurality of ribs 101b, 102b are formed on the inner faces of the lower case 101 and upper case 102 so as to secure oil flow channels at the outside of the filter member 103 and to reinforce the lower case 101 and upper case 102.
In this type of the oil strainer, as shown by oil flows F in FIG. 4, oil flows from the inflow opening 101a of the lower case 101 into the inner space of the pouch-like filter member 103, and passes through the filter 103. When the oil passes through the filter member 103, foreign matters such as abrasion powder produced in an automatic transmission and the like are trapped and removed (filtered), while the oil filtered out of the filter member 103 is discharged outside the case 100 from the outflow opening 102a of the upper case 102 (for example, refer to Japanese unexamined patent publication No. H09-327609).
For the conventional oil strainer as described above, occurrence of pressure loss by the filter member 103 is inevitable, however, it is desirable to render the other pressure loss than that by the filter member 103 as small as possible. However, size of the case 100, area of the filter member 103, width of the oil flow channel in the case 100, and opening position of the outflow opening 102a or the like are often restricted by the installation space of the oil strainer. Therefore, according to the conventional oil strainer, a turbulent flow ΔF such as whirlpool or the like is generated in the oil flow in a space ΔS behind the outflow opening 102a, and the turbulent flow ΔF interferes with the normal flow F directing to the outflow opening 102a, thereby to cause loss of flow, and the resultant oil flow channel resistance is recognized as one of the main causes of the increase in pressure loss.